The main objective of the proposed research is to elucidate the relationship between the process of the sexual differentiation of the brain and the hypothalamic regulation of food intake (FI) and body weight (BWt). We plan to identify those components of the regulation of FI and BWt which are sexually dimorphic, and to determine whether they are altered by the perinatal hormone environment and/or modulated in the adult by sex-specific hormones. In intact or gonadectomized male, female, androgenized female, and neonatally castrated males, FI, water intake, and BWt will be measured following chronic insulin treatment, forced exercise, growth hormone and prolactin injection. In addition, gastrin levels, the hypothalamic retention of C14 administered intragastrically as labelled glucose, and the diurnal distribution of actual feeding activity will be ascertained in these animal preparations. Analyses of these data will permit the identification of sexually differentiated parameters. The neural site of androgen action will be determined by stereotaxic implantation and timed removal of the hormone in the hypothalamus of the neonatal rat. In the adult rat, attempts will be made to elucidate the site of action of estrogen and growth hormone in the regulation of FI and BWt. Hormones will be applied directly to the brain and the techniques of lesioning and deafferentation will be employed to localize the site of action of the hormones. It is hoped that the study of both the development and adult functioning of the neural structures which regulate behavior and BWt will prove particulary valuable in promoting general understanding of this complex area of physiology.